The present invention relates to an optical fiber, optical amplification/oscillation device, laser light generating device, laser display unit, and color laser display unit, and more particularly to an optical fiber capable of operating as a fiber laser, and an optical amplification/oscillation device, laser light generating device, laser display unit, and color laser display unit each employing the optical fiber.
There has been proposed a color laser display unit for displaying a color image by the combination of lasers for emitting red laser light, green laser light, and blue laser light.
As the lasers for emitting red laser light and green laser light, the development of semiconductor lasers is proceeding. Further, a continuous-wave laser having an output of 10 W is now available by a solid-state laser for green laser light.
On the other hand, various studies have been made on the laser for emitting blue laser light. For example, a compound semiconductor laser containing nitrides typically such as gallium nitride (GaN) and method employing a nonlinear element for converting infrared laser light in a 920 nm band, for example, into a second harmonic to obtain blue laser light have been considered.
The above method employing a nonlinear element for converting infrared laser light into a second harmonic utilizes a nonlinear phenomenon, so that it is necessary to ensure a sufficient intensity of infrared laser light entering the nonlinear element.
A fiber laser using an optical fiber having a double-cladding structure has been proposed to obtain laser light in a 1050 nm band or in a 1550 nm band.
FIG. 1 is a schematic perspective view of an optical fiber 1 having a double-cladding structure, configuring the above fiber laser.
The optical fiber 1 has a core 10, a first cladding 11 formed so as to surround the core 10, and a second cladding 12 formed so as to surround the first cladding 11.
The core 10 is formed of glass doped with Er3+ or Nd3+, for example. The following description is applied to the case where the core 10 is formed of glass doped with Nd3+.
When pump light PL having a wavelength of 810 nm emitted from a semiconductor laser, for example, is coupled into the first cladding 11, laser light in a 1050 nm band, for example, is generated due to 4F3/2→4I11/2 transition as an example of the transitions of an energy state of Nd3+ in the glass.
On the other hand, signal laser light SL as light to be amplified, having a wavelength of 1050 nm is coupled into the core 10 simultaneously with the pump light PL, so that the signal laser light SL having the wavelength of 1050 nm can be amplified in the optical fiber 1 to thereby obtain high-intensity laser light in the 1050 nm band.
However, a blue light source as in a color laser display unit employs light having a 920 nm band so as to obtain light having a 460 nm band as a blue region after converting the light in the 920 nm band into a second harmonic. Accordingly, the light in the 1050 nm band is not required, and it is desirable to suppress the oscillation in the 1050 nm band. However, in the optical fiber whose core is doped with Nd3+ as mentioned above, the oscillation in the 1050 nm band is much intensive than the oscillation in the 920 nm band, and it is therefore very difficult to suppress the oscillation in the 1050 nm band and simultaneously effect the oscillation and amplification in the 920 nm band.
In the optical fiber capable of operating as a fiber laser in the case that there are a plurality of transition wavelength bands each allowing the oscillation of light, it is unknown that the oscillation in one of the transition wavelength bands is suppressed and the oscillation and amplification in another transition wavelength band are effected.